The senior senator from Missouri has doctors, scientists and nuclear nonproliferation advocates across the nation frustrated and perplexed.

The reason: He is single-handedly holding up a bill aimed at ending U.S. dependence on unpredictable foreign sources of medical isotopes. The isotopes are the essential radioactive material used in about 20 million scans of bones, hearts and other organs performed in the United States every year.

The legislation also would put an end to U.S. exports of the highly enriched uranium that is used to make medical isotopes, but that can easily be converted into bombs.

Bond says the export ban would jeopardize U.S. isotope supplies.

“My primary concern is ensuring the millions of cancer patients get the cures they need, and this bill puts their treatment at risk,” he said.

So far, no one appears to be backing Bond’s position.

Opposing him is practically every professional group dealing with nuclear medicine, along with groups trying to halt the proliferation of nuclear weapons.

They say that Bond is just plain wrong. Or that he’s playing politics, perhaps trying to position the University of Missouri’s research reactor to become the key domestic supplier of the isotopes.

“We don’t think this is a bill that would cripple us,” said Michael Graham, director of nuclear medicine at the University of Iowa and past president of the Society of Nuclear Medicine.

“It’s a fairly unique opportunity for us to build a domestic isotope supply,” he said. “We’ve been doing what we can to convince (Bond) of that.”

This has been a rough couple of years for doctors like Graham.

Two aging reactors in Canada and the Netherlands provide most of the U.S. supply of molybdenum-99, which is used to create the most commonly used isotope for medical tests. And both reactors were shut down for months at a time for repairs.

Scans that use the isotope are essential for diagnosing cancers and infections and for determining how well the heart handles stress. No U.S. reactors make the isotope.

For about 18 months, hospitals rationed the precious stuff. Scans were rescheduled or postponed. Patients received smaller doses and spent more time lying under scanners. Or they received a different isotope that exposed them to more radiation.

But help seemed to be on the way.

In November, the House of Representatives passed the American Medical Isotopes Production Act on a 400-17 vote, an incredible margin for a politically polarized Congress.

The legislation would authorize $163 million to help build isotope production facilities in the United States that would not require highly enriched uranium. That would ensure a safe, uninterrupted supply, bill supporters say.

It also would set a timetable for ending U.S. exports of highly enriched uranium to other countries for making medical isotopes. That addressed the concerns of nuclear nonproliferation advocates who want to keep the uranium out of the hands of terrorists.

The United States currently ships highly enriched uranium just to Canada’s Chalk River reactor in Ontario, although exports to other countries are still permitted.

Supporters assumed the isotope production act would sail through the Senate. Instead, Bond put a hold on the measure to keep it from going to debate.

In a letter to his congressional colleagues, Bond said the legislation put a legally binding cut-off date on exports of highly enriched uranium but offered no guarantee that U.S. patients would continue to get their treatments.

“Let me be clear that I support finding new ways to produce medical isotopes, especially from domestic sources,” Bond wrote.

“However, I am unaware of any type of comprehensive planning or documentation that describes in detail exactly who is expected to supply medical isotopes in sufficient quantities to meet the needs of U.S. medical patients without disruption…”

There is no way the legislation would jeopardize U.S. medicine, bill supporters say.

Isotope production in the United States would begin years before exports of highly enriched uranium were scheduled to end, the supporters say. And if U.S. production were delayed, the bill would allow Congress to postpone the export ban.

“I just think he’s misinformed,” said Alan Kuperman, a political scientist at the University of Texas and senior policy analyst for the Nuclear Control Institute. “It’s sort of an embarrassment.”

Kuperman said the medical isotope production act was the product of unprecedented cooperation between the medical and nuclear nonproliferation communities.

The two groups had clashed for years over allowing exports of highly enriched uranium, or HEU.

“It was divisive and nonproductive and led us to the current situation, shortages of medical isotopes and HEU still being exported,” Kuperman said. “A few years ago those two communities realized they were better off working together.”